A high dielectric constant (so-called “high-k”) film has been recently investigated as a component in a semiconductor device. Representative examples of a high-k material include Zr- and Hf-containing oxides. Such a material can be used for a dielectric film in a capacitor or a gate insulating film in an MOSFET to achieve good device performance which has not been obtained by the prior art.
Japanese patent application NO. 2002-373945 discloses a capacitor comprising such a high-k material. Therein, a dielectric film made of the high-k material is formed by atomic layer deposition (ALD). The ALD process in which one-atomic layers are deposited one by one has advantages that a deposition process may be conducted at a lower temperature and that a film with good film properties may be obtained.
FIG. 2 shows a cross-sectional view of the capacitor described in Japanese patent application NO. 2002-373945. Therein, on a substrate 21 are formed a device separating region 22 while in a device region is formed a transistor consisting of a gate electrode 23 and a source/drain diffusion layer 24. On both sides of the gate electrode 23, there are formed side walls 25. An unshown cobalt silicide film covers over the gate electrode 23 and the source/drain diffusion layer 24.
On the transistor is formed a bit line 29 via a cell contact 28. On the transistor is formed a cylindrical MIM capacitor via a capacitor contact 31. The capacitor has a structure that there are laminated a lower electrode 34, a dielectric film 35 and an upper electrode 36 are deposited, on which a tungsten film 37 is formed. An insulating film for the dielectric film 35 is made of a metal material such as ZrO2. The dielectric film 35 is deposited by atomic layer deposition.
When forming a ZrO2 film by atomic layer deposition, deposition gas used generally comprises ZrCl4 and H2O. The above reference has also described that a ZrO2 layer can be formed by the method. There have been, however, increased needs for a high-k film with much higher film properties and for a deposition process with a higher production efficiency. Any deposition process according to the prior art cannot adequately meet the needs. Furthermore, it has been strongly needed that a leak current is reduced in a capacitor comprising a high-k material.
Furthermore, there have been attempts to use a high-k material for a gate insulating film in a transistor. Using such a material, a film can be thin as calculated as a silicon oxide film even when making a gate insulating film thicker to some extent, so that a physically and structurally stable gate insulating film can be achieved. However, in a transistor comprising such a gate insulating film, dopants introduced in a gate electrode may sometimes penetrate the gate insulating film to reach a channel region. Dopant penetration may significantly deteriorate reliability of a semiconductor device without transistor properties as designed. In designing a transistor comprising a high-k gate insulating film, adequately preventing such dopant penetration is an important technical problem.
In view of the above situation, an objective of this invention is to give a semiconductor device comprising a film made of a high dielectric constant material with a reduced leak current in the film and with improved device reliability.
Another objective of this invention is to provide a capacitor with a higher capacity and a reduced leak current.
A further objective of this invention is to provide a transistor comprising a gate insulating film with a smaller thickness as calculated as a silicon oxide film and with improved reliability.